title: Neuroepithelial endocrine cells in the lung of the lungfish Protopterus aethiopicus. An electron- and fluorescence-microscopical investigation.
abstract: The occurrence and distribution of neuroepithelial endocrine (NEE) cells was demonstrated electron- and fluorescence-microscopically in the lungfish Protopterus aethiopicus. They were only found to occur solitarily in the basal part of the cilio-mucous epithelium which is restricted to the pneumatic duct and adjacent parts of the common anterior chamber. The NEE cells show a yellow, formaldehyde-induced fluorescence. Electron-microscopically, all the NEE cells are characterized by membrane-bound electron-dense secretory granules with varying diameters, ranging from 75 to 150 nm. These granules are distributed throughout the cytoplasm with a higher concentration in the basal region. The NEE cells were regularly found to contain paracrystalline inclusions with a tubule-like substructural arrangement. A small part of the NEE cells appeared to reach the luminal surface by means of a long slender process bearing specialized beaded microvilli on its apical pole. Intraepithelial nerve fibres, with the ultrastructural characteristics of afferent fibres, were found running parallel to the airway surface. Nerve profiles, largely resembling the latter, can be seen in the proximity of the basolateral plasma membrane of the NEE cells. In addition, nerve terminals containing an aggregation of small clear vesicles are in close contact with the NEE cells. In conclusion, it appears that, as has so far been assumed in higher vertebrates, the NEE cells in the lung of Protopterus may perceive changes in the airway gases whereupon they could respond by releasing a chemical modulator, influencing contacting afferent nerve terminals or nearby smooth muscle bundles. Furthermore, intraepithelial nerve fibres or NEE cells might be stretch-sensitive.
authors.affiliation: Institute of Histology and Microscopic Anatomy, University of Antwerp, Belgium.
authors.forename: D
authors.initials: D
authors.lastname: Adriaensen
authors.forename: D W
authors.initials: DW
authors.lastname: Scheuermann
authors.forename: J P
authors.initials: JP
authors.lastname: Timmermans
authors.forename: M H
authors.initials: MH
authors.lastname: De Groodt-Lasseel
mesh_terms: D000818:Animals; D003594:Cytoplasmic Granules / Q000648:ultrastructure; D004847:Epithelial Cells; D004848:Epithelium / Q000648:ultrastructure; D005399:Fishes / Q000033:anatomy & histology*; D007150:Immunohistochemistry; D008168:Lung / Q000166:cytology* / Q000294:innervation; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009412:Nerve Fibers / Q000648:ultrastructure; D009490:Neurosecretory Systems / Q000166:cytology* / Q000648:ultrastructure